Long life, high current density cathodes

Research undertaken at Hughes Electron Dynamics Division which is directed toward the development of long life, high current density cathodes will be outlined and discussed. Requirements for 7 to 10 years of operating life at high current densities, 1 amp/cm²and higher, are pushing the limits of known cathode technology. The most reliable cathode for high current density convergent gun applications presently available is the tungsten-barium dispenser cathode. The performance of this type of cathode, however, is known to degrade with age at a rate that is strongly dependent on temperature. Life test data taken at Hughes EDD can be understood in terms of an aging model, based on surface depletion of the cathode which is controlled by the time dependence of the Knudsen flow. This aging model, along with experiments, guided in part by the prediction of this model, are discussed.